Device for manufacturing semiconductor device and method of manufacturing the same

ABSTRACT

There is provided a clustered device for manufacturing a semiconductor device in which a cleaning chamber, a rapid thermal processing chamber, an optical measurement chamber, and the like are arranged around a load-lock room. In an optical measurement system, there are disposed an exciting light source, a measuring light source, a light detector, a control/analyze system, and the like. During the formation of an oxide film, for example, a wafer is cleaned in the cleaning chamber and then the amount of a natural oxide film remaining on the wafer or the like is measured by optical modulation reflectance spectroscopy in the optical measurement chamber. Thereafter, the wafer is oxidized in the rapid thermal processing chamber. As a result, the surface of the wafer is prevented from being oxidized on exposure to an atmosphere and the surface state of the wafer can be monitored in the course of a sequential process steps. By measuring the thickness of a film on a semiconductor region by optical evaluation in the clustered manufacturing device, the manufacturing process using the clustered device can be controlled.

BACKGROUND OF THE INVENTION

The present invention relates to a device for manufacturing asemiconductor device and a method of manufacturing the same. Moreparticularly, it relates to property control of a surface of asemiconductor layer and a film formed thereon in a manufacturing processperformed by using a clustered manufacturing device in an atmosphereinsulated from an external space.

As the packaging density of a semiconductor integrated circuit hasincreased in recent years, miniaturization and higher performance havebeen required of an element composing a MOS device, such as atransistor. However, the miniaturization of an element such as atransistor should not reduce the reliability of the whole device.Therefore, both miniaturization and increased reliability are requiredof each component of an element such as a transistor.

In particular, a gate insulating film (gate oxide film), which is anessential component of a MOS device, has rapidly been reduced inthickness. It is expected that an extremely thin insulating film with athickness of 4 nm or less will be used in the twenty-first century.Since the properties of the gate insulating film are said to determinethe properties of the MOS transistor and the electric properties of asemiconductor integrated circuit, the formation of an insulating filmwith excellent properties has been in great demand.

It has been proved that the properties of an insulating film are largelydependent on the surface state of a semiconductor layer before theinsulating film is formed thereon. Accordingly, there has been studied acleaning method for improving the properties of the semiconductor layeror the like. For example, it has been reported that the use of acleaning method (pregate cleaning process) which minimizes theundulations of a surface of a Si substrate allows the formation, on thelaboratory level, of a high-quality gate oxide film with an extremelysmall thickness of about 1.2 nm.

There has also been reported a clustered manufacturing device whichallows sequential process steps from pregate cleaning to gate insulatingfilm formation to be performed without exposing wafers to an atmosphereand thereby prevents the formation of a natural oxide film and thedeposition of a contaminant resulting from exposure to the atmosphere(Document 1: Schuegraf et. al., IEEE/International Reliability andPhysics Symposium 97, p. 7). It has been proved that a high-quality gateinsulating film can be formed by the manufacturing process using theclustered manufacturing device. The use of the clustered manufacturingdevice is particularly desirable in the step of forming a gateinsulating film having a reduced thickness of 4 nm or less.

On the other hand, property control of the gate insulating film in a MOSdevice has been performed conventionally by forming an element such as aMOS capacitor or MOS transistor and analyzing the electric properties ofthe element. If any trouble occurs in the step of forming the gateinsulating film, the procedure is followed in which the trouble is foundby evaluating the electric properties of the MOS capacitor or the likethat has been formed previously, diagnosing the cause of the trouble,and practicing a troubleshooting method. As a result, a large quantityof gate insulating films with degraded electric properties are formedconsecutively till the trouble is found, which reduces productionefficiency.

If an ellipsometer used conventionally for measuring a film thickness inthe manufacturing process is used to measure the thickness of a thinfilm, it does provide a measured value, but the minimum film thicknessthat can be measured with reliability is on the order of 10 nm. It canhardly be said that a film thickness smaller than 10 nm is measurablewith sufficiently high accuracy. Thus far, a reliable evaluation methodwhich is usable for an extremely thin film with a thickness of about 4nm or less in the manufacturing process has not been established yet.

Although the electric properties of a MOS capacitor or the like formedon a wafer are measured after a large number of sequential process stepswere performed with respect to the wafer in the process using theclustered manufacturing device described above, there is no method ofcontrolling the condition of the wafer in the course of the processsteps. Despite the fact that a high-quality gate insulating film isformable on the laboratory level, there is no guarantee, under presentcircumstances, that high-quality gate insulating films can be formed inthe process of mass-producing MOS devices even by using the clusteredmanufacturing device.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide amethod of manufacturing a semiconductor device incorporating an opticalevaluation method which can provide sufficient reliability and accuracyin measuring the properties of an extremely thin film.

A second object of the present invention is to provide a method anddevice for manufacturing a semiconductor device which allow opticalmeasurement of the properties of an insulating film, especially thethickness thereof, and provide a method of property control insequential process steps from pregate cleaning to insulating filmformation, which are performed by using a clustered manufacturingdevice.

A device for manufacturing a semiconductor device of the presentinvention is a clustered device comprising: a plurality of processingrooms for processing a wafer having a semiconductor region; a sharedcontainer enclosing a space containing the plurality of processing roomssuch that the space is held in an atmosphere disconnected from anexternal space; transporting means for transporting the wafer within theshared container; and optical measuring means for optically evaluating asurface state of the wafer being disposed at any site in the sharedcontainer.

The arrangement allows optical evaluation of the surface state of awafer in a situation unaffected by a natural oxide film formed on thewafer or contamination deposited thereon by exposing the wafer to theexternal space. By thus optically evaluating the surface state of thewafer after the removal of the film or after the formation of the film,the thickness of an oxide film or the like can be measured with highaccuracy. Since the wafer need not be extracted, for optical evaluation,to the outside of the shared container, the process of manufacturing asemiconductor device can be controlled properly by using in-lineevaluation without adversely affecting the wafer in the manufacturingprocess.

In the device for manufacturing a semiconductor device, the opticalmeasuring means can be comprised of: a first light source for generatingexciting light; a second light source for generating measuring light; afirst light guiding member for intermittently irradiating thesemiconductor region of the wafer in the shared container with theexciting light generated from the first light source; a second lightguiding member for irradiating the semiconductor region with themeasuring light generated from the second light source; reflectancemeasuring means for measuring the reflectance of the measuring lightwith which the semiconductor region is irradiated; a third light guidingmeans for causing the measuring light reflected by the semiconductorregion to be incident upon the reflectance measuring means; and changecalculating means for receiving an output of the reflectance measuringmeans and calculating a change rate of reflectance of the measuringlight by dividing the difference between the reflectances of themeasuring light when the semiconductor region is irradiated and notirradiated with the exciting light by the reflectance of the measuringlight when the semiconductor region is not irradiated with the excitinglight.

This achieves the following effect. When the semiconductor region isirradiated with the exciting light guided by the first light guidingmember, carriers in the semiconductor region are excited to produce anelectric field. Under the influence of the electric field, thereflectance of the measuring light guided to the semiconductor region bythe second light guiding member changes in the presence or absence ofthe radiation of exciting light. The change rate varies based on themagnitude of the intensity of the electric field and on the wavelengthof the measuring light. If a defect serving as the center ofrecombination for carriers exists in a near-surface portion of thesemiconductor region, the lifespan of the excited carriers is reduced,so that the intensity of the electric field formed by carriers isreduced. That is, the change rate of reflectance in the presence orabsence of the radiation of exciting light changes based on the numberof defects present in the near-surface portion of the semiconductorregion. If there is a film on the semiconductor region, the process ofcapturing electrons proceeds with an increase in the thickness of thefilm so that the change rate of reflectance increases. If the changerate of reflectance of the measuring light in the semiconductor regionis calculated by the change calculating means from the value measured bythe reflectance measuring means, the change rate of reflectance includesdata on the crystallized state of the semiconductor region, on thepresence or absence of a film, or on the thickness of the film. Based onthe change rate of reflectance, therefore, the surface state of thewafer can be evaluated with high sensitivity.

In the device for manufacturing a semiconductor device, the plurality ofprocessing rooms include a processing room for performing a cleaningprocess involving an etching effect with respect to the wafer and aprocessing room for forming a film on the semiconductor region of thewafer. The arrangement allows optical evaluation in the situation inwhich the film has been removed from the wafer or in which a film hasbeen formed on the wafer thereafter, thus allowing optical evaluation ofthe cleaned wafer surface without the natural oxide film.

The device for manufacturing a semiconductor device can further comprisean optical measurement room provided within the shared container,wherein the optical measuring means is disposed in the opticalmeasurement room.

In the device for manufacturing a semiconductor device, the processingroom for forming a film on the wafer is so constructed as to form anoxide film by performing a thermal oxidation process with respect to thesemiconductor region of the wafer, the clustered device furthercomprising a processing room for forming a conductor film on the oxidefilm, the processing room being provided within the shared container.The arrangement allows the formation of the conductor film on the waferformed with the thermal oxide film without exposing the wafer to theexternal space. Consequently, there can be formed a semiconductor devicesuch as a MOS transistor having an oxide film with a small thicknesswhich is controlled with high accuracy.

A first method of manufacturing a semiconductor device of the presentinvention includes formation of a film on a semiconductor region of awafer or removal of a film from a surface of the semiconductor region ofthe wafer, the method comprising the steps of: (a) irradiating thesemiconductor region of the wafer with measuring light; (b)intermittently irradiating the semiconductor region of the wafer withexciting light; and (c) calculating a change rate of reflectance bydividing the difference between the reflectances of the measuring lightwhen the semiconductor region of the wafer is irradiated and notirradiated with the exciting light by the reflectance of the measuringlight when the semiconductor region is not irradiated with the excitinglight, wherein the thickness of the film is determined based on thechange rate of reflectance.

In accordance with the method, data on the thickness of a film formed onthe semiconductor region can be obtained by evaluation based on opticalmodulation reflectance spectroscopy by utilizing the phenomenon that thepresence of the film in the semiconductor region under measurementperformed by optical modulation reflectance spectroscopy causes theprocess of capturing electrons with an increase in the thickness of thefilm and hence increases the change rate of reflectance. In themeasurement performed by ellipsometry currently used, a measurementerror becomes extremely large or measurement sensitivity cannot beobtained at all if the film thickness is reduced to 4 nm or less. Bycontrast, optical modulation reflectance spectroscopy allows precisemeasurement of the thickness of such a thin film.

In the first method of manufacturing a semiconductor device, the step(c) includes producing a spectrum indicative of the change rate ofreflectance when the wavelength of the measuring light is varied anddetermining the thickness of the film based on a peak value which is amaximum absolute value of the change rate of reflectance. This allowshigh-sensitivity measurement of the film thickness.

Alternatively, the step (c) includes producing a spectrum indicative ofthe change rate of reflectance when the wavelength of the measuringlight is varied and determining the thickness of the film based on apeak-to-peak value which is the difference between a positive maximumvalue of the change rate of reflectance and a negative maximum valuethereof. This allows highest-sensitivity measurement of the filmthickness.

In the first method of manufacturing a semiconductor device, the step(c) includes determining the thickness of the film based on the changerate of reflectance at a constant wavelength close to the wavelength ofthe measuring light indicative of a peak value which is a maximumabsolute value of the change rate of reflectance. This reduces the timerequired for the measurement of the film thickness.

In the first method of manufacturing a semiconductor device, even whenthe thickness of the film is 2 nm or less, which cannot be measured bythe conventional optical measurement method, the film thickness can bemeasured with high sensitivity.

When the thickness of the film is 1 nm or less, in particular, theoptical evaluation is performed with respect to a p-type semiconductorregion as the semiconductor region. This provides high measurementsensitivity and high measurement accuracy.

In the first method of manufacturing a semiconductor device, thethickness of the film is measured in each of a p-type semiconductorregion and an n-type semiconductor region as the semiconductor region.If the thickness of the film is measured to be 1 nm or less, the valuemeasured in the p-type semiconductor region is used as the thickness ofthe film. If the thickness of the film is measured to be over 1 nm, thevalue measured in the n-type semiconductor region is used as thethickness of the film. As a result, the thickness of an extremely thinfilm can be measured with highest sensitivity by using the phenomenonthat characteristics representing the relationship between the changerate of reflectance and the film thickness differ if the conductivitytype of the semiconductor region is different.

In the first method of manufacturing a semiconductor device, thesemiconductor region has preferably a resistivity of 0.1 Ωcm⁻¹ or less.

A second method of manufacturing a semiconductor device of the presentinvention is practiced by using a clustered device for manufacturing thesemiconductor device, comprising a plurality of processing rooms, ashared container enclosing a space containing the plurality ofprocessing rooms such that the space is held in an atmospheredisconnected from an external space, and transporting means fortransporting the wafer within the shared container, the methodcomprising the steps of: (a) forming a film on the wafer or removing afilm from a surface of the wafer in one of the plurality of processingrooms; and (b) determining the thickness of the film by opticallyevaluating a surface state of the wafer at any site in the sharedcontainer.

In accordance with the method, the thickness of the film on the wafercan be calculated by optical evaluation performed in the course ofsequential process steps continuously performed or when the sequence ofprocess steps are completed and an atmosphere of the external space isabout to be restored. This allows a judgment of whether conditions forone of sequential process steps or for the entire process stepsperformed in the clustered manufacturing device are appropriate or notor a pass/fail judgment of the film formed on the wafer.

In the second method of manufacturing a semiconductor device, the step(b) includes the substeps of: (x) irradiating a semiconductor region ofthe wafer with measuring light; (y) intermittently irradiating thesemiconductor region of the wafer with exciting light; and (z)calculating a change of reflectance by dividing the difference betweenthe reflectances of the measuring light when the semiconductor region ofthe wafer is irradiated and not irradiated with the exciting light bythe reflectance of the measuring light when the semiconductor region isnot irradiated with the exciting light, so that the thickness of thefilm is determined based on the change rate of reflectance.

The method allows the determination of the thickness of an extremelythin film or of the presence or absence thereof in a clustered device byusing the fact that data on the thickness of the film can be obtained byoptical modulation reflectance spectroscopy, as described above.

In the second method of manufacturing a semiconductor device, the step(a) includes removing a natural oxide film from a surface of the waferand the step (b) includes determining the thickness of the natural oxidefilm. As a result, an extremely thin natural oxide film with a thicknessof several nanometers can be removed optimally.

In the second method of manufacturing a semiconductor device, there isfurther provided the step of (c) controlling the time of processing suchthat the natural oxide film remaining on the wafer has a thickness equalto or smaller than a specified value. As a result, the thickness of thenatural oxide film can be held at a most preferred value.

In the second method of manufacturing a semiconductor device, the step(a) may include forming a gate insulating film on the wafer and the step(b) may include determining the thickness of the gate insulating film.

In the second method of manufacturing a semiconductor device, the step(a) may further include forming, on the gate insulating film, aconductor film for a gate electrode and the method may further comprise,after the step (b), the step of (c) controlling the thickness of thegate insulating film based on the change rate of reflectance calculatedin the step (b) prior to the formation of the conductor film for a gateelectrode.

In the second method of manufacturing a semiconductor device, the step(b) preferably includes measuring the change rate of reflectance in eachof the p-type semiconductor region and the n-type semiconductor regionand determining the thickness of a natural oxide film based on thedependent property of the p-type semiconductor region or the n-typesemiconductor region providing the higher change rate of reflectance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram diagrammatically showing a structure of aclustered device for manufacturing a semiconductor device used in eachof first to third embodiments of the present invention;

FIG. 2 is a cross-sectional view schematically showing a structure of anoptical measurement mechanism used in each of the first to thirdembodiments;

FIG. 3 is a spectral diagram showing reflectances measured by opticalmodulation reflectance spectroscopy in the first embodiment;

FIG. 4 shows data indicative of the relationship between a cleaning timeand a peak value of a spectrum obtained by optical modulationreflectance spectroscopy;

FIG. 5 is a spectral diagram showing the reflectances of various oxidefilms measured by optical modulation reflectance spectroscopy;

FIG. 6 shows data indicative of the relationship between a filmthickness determined by TEM observation and a peak value of a spectrumobtained by optical light modulation reflectance spectroscopy;

FIG. 7 is a TEM micrograph of a cross-sectional structure in which anoxide film and a polysilicon film are deposited on a silicon substrate;

FIG. 8 is a spectral diagram showing a basic configuration obtained byoptical modulation reflectance spectroscopy in accordance with thepresent invention;

FIG. 9 is a cross-sectional view schematically showing a structure usedwhen optical measurement is performed in a single isolated chamberaccording to a fourth embodiment of the present invention;

FIG. 10 shows data indicative of the relationship between a filmthickness determined by TEM observation and a peak-to-peak value of aspectrum obtained by optical modulation reflectance spectroscopy in afifth embodiment of the present invention;

FIG. 11 shows spectra obtained from actual measurement performed in ann-type semiconductor region by optical modulation reflectancespectroscopy in the fifth embodiment;

FIG. 12 shows data indicative of variations in leakage current in a gateoxide film controlled in accordance with a method of controlling thethickness of a gate oxide film in the fifth embodiment;

FIG. 13 shows data indicative of variations in the peak-to-peak value ofa spectrum obtained by optical modulation reflectance spectroscopyplotted against a cleaning time when wafers are cleaned by using aclustered device according to the fifth embodiment, which is shown inFIGS. 1 and 2;

FIG. 14 is a cross-sectional view showing an exemplary structure inwhich an optical measurement system is disposed collectively on theceiling side of a chamber in another embodiment of the presentinvention;

FIG. 15 is a cross-sectional view showing an exemplary structure inwhich measuring light is incident at an large angle on an object undermeasurement in still another embodiment of the present invention;

FIG. 16 is cross-sectional view showing an exemplary structure in whichan optical measurement system is disposed more integrally on the ceilingside of a chamber in still another embodiment of the present invention;

FIGS. 17a to 17 c are cross-sectional views illustrating a manufacturingprocess for performing sequential process steps from cleaning to gateinsulating film formation with respect to a wafer without using aclustered manufacturing device;

FIGS. 18a to 18 c are cross-sectional views illustrating an example of amanufacturing process for performing sequential process steps fromcleaning to gate insulating film formation with respect to a wafer byusing a clustered manufacturing device; and

FIGS. 19a to 19 d are cross-sectional views illustrating another exampleof the manufacturing process for performing sequential process stepsfrom cleaning to gate insulating film formation with respect to a waferby using a clustered manufacturing device.

DETAILED DESCRIPTION OF THE INVENTION Process Performed in ClusteredManufacturing Device

Prior to the description of a device for manufacturing a semiconductordevice according to the embodiments of the present invention, adescription will be given to a method not using a clusteredmanufacturing device and a method using a clustered manufacturing devicein performing sequential process steps from cleaning to gate insulatingfilm formation.

FIGS. 17a to 17 c are cross-sectional views illustrating the method notusing the clustered manufacturing device. FIG. 17a shows a wafer priorto cleaning. As shown in FIG. 17a, a natural oxide film has been formedon a semiconductor region. Then, in the step shown in FIG. 17b, cleaningfor removing the oxide film, i.e. , acid treatment or the like isperformed. In the step, cleaning with ammonium is conductedintentionally to form a chemical oxide film on the semiconductor region.Next, in the step shown in FIG. 17c, a thermal oxidation process or thelike is performed to form an oxide film on the semiconductor region viathe chemical oxide film.

On the other hand, FIGS. 18a to 18 d are cross-sectional viewsillustrating an example of the method using the clustered device formanufacturing a semiconductor device. FIG. 18a shows a wafer carried inthe clustered device for manufacturing a semiconductor device. A naturaloxide film has been formed on a semiconductor region, similarly to thefirst method. Then, in the step shown in FIG. 18b, cleaning for removingthe oxide film, i.e., acid treatment or the like is performed. In thestep, the natural oxide film is removed completely so that the surfaceof the semiconductor region is exposed. Next, in the step shown in FIG.18c, a thermal oxidation process or the like is performed to form a gateinsulating film on the semiconductor region.

FIGS. 19a to 19 d are cross-sectional view illustrating another exampleof the method using the clustered device for manufacturing asemiconductor device. In the process illustrated in FIGS. 19a to 19 d,basically the same process as illustrated in FIGS. 18a to 18 d isperformed. In this example, however, an extremely thin oxide film isformed on the semiconductor region, as shown in FIG. 19c. In addition, athermal oxidation process or the like is performed in the step shown inFIG. 19d, so that a gate oxide film is formed on the semiconductorregion.

Each of the following first and second embodiments has performedsequential process steps from cleaning to oxide film formation by usingeither one of the methods illustrated in FIGS. 18a to 18 c and in FIGS.19a to 19 d.

EMBODIMENT 1 Structure of Clustered Chamber

FIG. 1 is a block diagram diagrammatically showing a structure of aclustered device for manufacturing a semiconductor device according tothe present embodiment. In FIG. 1 are shown: a cleaning chamber 1; arapid thermal processing chamber 2; a load-lock room 3; a wafer coolingchamber 4; an optical measurement chamber 5; and a wafer load/unloadport 6. That is, the load-lock room 3 and the individual chambers 1, 2,4, and 5 mounted thereon like clusters function as a shared containerenclosing a space in an atmosphere under reduced pressure which isdisconnected from an external space, thereby forming a so-calledclustered manufacturing device. In the step of forming an oxide film,e.g., wafers are cleaned in the cleaning chamber 1 and subsequentlyoxidized in the rapid thermal processing chamber 2. At this time, thenatural oxide films on the wafers are removed in the wafer cleaningstep. The load-lock room 3 is so structured as to optimize the transferof the wafers to be processed and the inside of the load-lock room 3 isunder reduced pressure. Accordingly, the surfaces of the wafers areprevented from being exposed to an atmosphere and thereby oxidized evenafter the cleaning step is completed.

The present embodiment is characterized in that the optical measurementchamber 5 is disposed in the shared space of the clustered manufacturingdevice and that an exciting light source 7 (Ar ion laser), a measuringlight source 8 (150 W Xe lamp), an optical detector 9 for measuring theintensity of reflected measuring light, optical fibers 10, 11, and 12serving as light guiding paths between the optical measurement chamber 5and the exciting light source 7, measuring light source 8, and opticaldetector 9, respectively, and a control/analyze system 13 forcontrolling equipment and calculating/analyzing data during measurementby optical modulation reflectance spectroscopy.

Optical Measurement System

FIG. 2 is a perspective view schematically showing an opticalmeasurement system disposed in the device for manufacturing asemiconductor device.

In FIG. 2 are shown: a wafer stage 21; a wafer 22; a quartz window 23;an incident measuring light inlet 24; a reflected measuring light outlet25; an exciting light inlet 26; a light shield plate 27 for blockingstray light which is the exciting light incident on the wafer 22 andreflected thereby; and a signal line 30 for providing a connectionbetween the exciting light inlet 26 and the control/analyze system 13.Each of the incident measuring light inlet 24, reflected measuring lightoutlet 25, and exciting light inlet 26 has the function as an opticalfiber supporter. The exciting light inlet 26 is provided with anadditional chopper for intermittently irradiating an object undermeasurement with the exciting light at a frequency of 500 Hz, though itis not shown in the drawing. The chopper is controlled by thecontrol/analyze system to operate in synchronization with the opticaldetector 9. Thus, the device for manufacturing a semiconductor deviceaccording to the present embodiment is so structured as to form ahigh-quality gate insulating film without trouble by controlling themanufacturing process, while optically monitoring the wafer insequential process steps from cleaning to gate insulating filmformation.

Principle of Measurement by Optical Modulation Reflectance Spectroscopy

Hereinafter, the principle of measurement by optical modulationreflectance spectroscopy will be described with reference to thestructure of the measurement system of the present embodiment shown inFIG. 2. The exciting light generated from the exciting light source 7 issupplied into the optical measurement chamber 5 via the additionalchopper provided in the exciting light inlet 26 for intermittentirradiation of the semiconductor region of the wafer 22. In the presentembodiment, the semiconductor region is of n-type. The value (ΔR/R)obtained by dividing, by the intensity R of reflected measuring lightwhen the semiconductor region is not irradiated with the exciting light,the difference ΔR between the intensities of reflected measuring lightwhen the semiconductor region is irradiated and not irradiated withexciting light is detected as the change rate of reflection intensity bythe control/analyze system 13. Variations in the change rate ofreflection intensity are monitored by the foregoing structure. It isunnecessary to dispose a polarizer at the measuring light incident sideand an analyzer at the measuring light reflecting side, unlike the casewhere measurement is performed by using an ellipsometer. However, it ispossible to add the function of ellipsometry by optionally disposing thepolarizer and analyzer.

The foregoing change rate (ΔR/R) of reflection intensity is obtained bythe following action. In general, the irradiation of a semiconductorregion with light increases the number of carriers excited by the light.When the carriers return to the original energy level thereafter, theyemit light and disappear. As the number of carriers changes, theintensity of an electric field changes in the area of the semiconductorregion irradiated with the exciting light. Accordingly, the intensity ofreflected measuring light in the presence of the radiation of excitinglight is different from that in the absence of the radiation of excitinglight. If a large number of defects exist in a near-surface portion ofthe semiconductor region, however, an interface state at a low energylevel is produced by the defects. Since the defects forming such aninterface state function as a layer for capturing the carriers, if thecarriers excited under the radiation of light are captured by thedefects and cannot reach a sufficiently high energy level or if thecarriers excited to a high energy level are captured by the defects, theintensity of light generated when the excited carriers return to a lowerenergy level is reduced. As a result, the intensity of the electricfield in the area of the semiconductor region irradiated with theexciting light changes. Accordingly, the change rate (ΔR/R) ofreflection intensity also changes depending on the number of capturelevels in the near-surface portion of the semiconductor region. If afilm exists on the semiconductor region and the capturing of electronsin the near-surface portion of the semiconductor region is remarkable, avariation in the change rate (ΔR/R) of reflectance increases. Therefore,data on a physical state in the near-surface portion of thesemiconductor region can be obtained by monitoring the change rate ofreflection intensity.

It is assumed that the frequency for chopping is related to the timeelapsed from the recombination of the carriers to the changing of theintensity of the electric field in the semiconductor region. It has beenproved experimentally that the frequency for chopping is preferably 1kHz or lower and, more preferably, 500 Hz or lower. In addition, thephoton energy of the exciting light is preferably larger than the bandgap of the semiconductor region. When a silicon substrate is used,exciting light at a wavelength with photon energy of 1.1 eV or more isused preferably. The foregoing statement holds true in each of theembodiments described later.

Since the radiation intensity of the measuring light (at each wavelengthrange) is assumed to be constant in the present embodiment, thedetection of reflection intensity is conducted as a substitute for thedetection of reflectance. Specifically, the measurement of the changerate of reflection intensity is performed by intermittently irradiatingthe semiconductor region of the wafer 22 with an Ar ion laser beam asthe exciting light, while continuously irradiating the semiconductorregion with a light beam from a Xe lamp as the measuring light, anddetecting a variation in the reflection intensity of the measuringlight. Briefly, the value (ΔR/R) obtained by dividing, by the reflectionintensity R when the semiconductor region is not irradiated with theexciting light, the difference ΔR between the reflection intensitieswhen the semiconductor region is irradiated with and not irradiated withthe exciting light is detected as the change rate of reflectance. Inshort, light modulation reflectance spectroscopy is a method ofexamining a spectral configuration obtained by varying the wavelength ofprobe light, while repeatedly and intermittently performing irradiationwith the exciting light, and measuring the change rate of reflectance ateach wavelength (energy value of light) of the probe light.

FIG. 8 is a spectral diagram in a basic pattern representing therelationship between the value of photon energy which is proportional tothe reciprocal of the wavelength λ of probe light incident upon asingle-crystal silicon layer as the semiconductor region and the changerate (ΔR/R) of reflectance. The change rate (ΔR/R) of reflectance shownin FIG. 8 is a relative value which is zero in the initial state. Theregion in which the change rate (ΔR/R) of reflectance varies mostremarkably is adjacent the negative peak value shown in FIG. 8.Therefore, the present embodiment assumes that a peak value indicatesthe negative peak value and uses 376 nm corresponding to about 3.30 eVas the wavelength of the probe light at the negative peak value, whichis approximately equal to an energy value indicative of the negativepeak value. In the foregoing description, the distance between thenegative peak value and the positive peak value is termed “peak-to-peakvalue”.

In obtaining the spectral configuration, it is preferable to detect andanalyze the spectrum of the probe light in the wavelength range of 200to 500 nm.

Control of Cleaning Step and Optical Measurement

A description will be given next to sequential process steps fromcleaning to gate insulating film formation, which is performed by usingthe device for manufacturing a semiconductor device and opticalmeasurement system described above.

First, product wafers including an advanced wafer (monitor wafer) aretransferred from the wafer load/unload port 6 into the load-lock room 3so that the natural oxide films on the wafers are removed. Each of thewafers is internally formed with an n-type semiconductor region having aresistivity of 0.02 Ωcm⁻¹ for high-sensitivity measurement. The pressureinside the load-lock room 3 has been reduced to about 50 mTorr. Theadvanced wafer is initially introduced from the load-lock room 3 intothe cleaning chamber 1 such that a surface of the wafer is cleaned byusing HF vapor and etched by using radicals produced by dissociating Cl₂gas under UV irradiation, whereby the natural oxide film is removed anda flat interface is formed. For this purpose, anticorrosive treatment orthe like has been performed with respect to the cleaning chamber 1.

At this stage, the wafer is temporarily carried in the opticalmeasurement chamber 5 so that the state of the semiconductor region isexamined by optical modulation reflectance spectroscopy described above.

FIG. 3 is a spectral diagram showing reflectance variations obtained asa result of optical modulation reflectance spectroscopy. In the drawing,the horizontal axis represents photon energy which is inverselyproportional to wavelength and the vertical axis represents ΔR/R. Asindicated by “SPECTRUM FROM PRE-CLEANING WAFER” in the drawing, the peakvalue of the spectrum from a pre-cleaning wafer obtained by opticalmodulation reflectance spectroscopy is high because of the thick naturalfilm formed on the semiconductor region. As indicated by“SPECTRUM FROMCHEMICAL OXCIDE FILM” in the drawing, it will be understood that aconsiderably thick oxide film exists even when a chemical oxide film isformed by a conventional method, though the peak value is smaller thanthe former case where the natural oxide film has been formed. Ifsufficient cleaning is not performed, a peak exists, though it isobscure, as indicated by “SPECTRUM FROM POST-CLEANING WAFER 2”. When anoxidation process was performed under this condition, a smaller numberof defects were observed in the subsequent reliability evaluation test.

When proper cleaning was performed, the peak of the spectrum obtained byoptical modulation reflectance spectroscopy was barely recognizable, asindicated by “SPECTRUM FROM POST-CLEANING WAFER 1” in the drawing. If anoxidation process was performed under this condition, it was proved thatdefects were seldom produced in the subsequent reliability test. Thus,it will be understood that measurement data obtained by reflectancespectroscopy is usable in judging whether or not the cleaning processinvolving the etching effect is proper.

FIG. 4 shows data indicative of the relationship between the cleaningtime and the peak value of the spectrum obtained by optical modulationreflectance spectroscopy. As shown in the drawing, the peak value isreduced as the cleaning time is increased, which indicates the completeremoval of the natural oxide film.

To say nothing of the case where a conventional unclusteredmanufacturing device is used, even when a clustered manufacturing deviceis used, if the oxidation step is performed after cleaning was performedfor an empirically determined time, the quality of a gate insulatingfilm may be degraded due to the slightly remaining natural oxide film.By contrast, the process using the manufacturing device according to thepresent embodiment allows the detection of presence or absence of anextremely thin oxide film on the semiconductor region prior to oxidationafter cleaning. As a result, the occurrence of trouble such as a faultygate insulating film can be prevented positively.

If the oxide film remaining on the wafer after cleaning is detected inthe optical measurement chamber 5, the wafer is placed again in thecleaning chamber 1 so that cleaning is performed appropriately for thetime required to remove the remaining oxide film. This saves the waferwhich might have failed if it had been processed in the subsequent stepand allows effective use of the wafer.

Although the present embodiment has set to 0.1 the peak value of thespectrum obtained by optical modulation reflectance spectroscopy, whichis used as a standard for a pass/fail judgment prior to oxidation, thestandard for evaluation need not necessarily be 0.1 since the standardfor evaluation is dependent on the S/N ratio of the measurement system.Instead, a standard for judgment suitable for an individualmanufacturing process can be used.

A chemical oxide film may also be formed intentionally after cleaning.In that case, if the proper range of the peak value of the spectrumobtained by optical modulation reflectance spectroscope ispredetermined, it becomes possible to control the manufacturing processby detecting a deviation from the proper conditions for themanufacturing process or adjusting the manufacturing conditions or thelike. Thus, the method of manufacturing a semiconductor device of thepresent invention is not limited to the clustered manufacturing device.If the clustered manufacturing device is used, however, the wafer cannotbe retrieved from the device till sequential process steps arecompleted. Hence, such optical evaluation as performed in the clusteredmanufacturing device in the present embodiment achieves the particularlyremarkable effect of judging whether each of the process steps currentlyperformed is proper or not. Since the surface state of the wafer is notaffected by environmental conditions outside the device (the presence ofoxygen, moisture, or the like), the present invention is advantageous inthat it can determine the thickness of a thin oxide film with athickness of 10 nm or less, while removing the influence of a naturaloxide film or the like, thereby achieving higher measurement accuracy.

Although the present embodiment has provided the rapid thermalprocessing chamber 2 to perform an oxidation process with respect to thewafer, the present invention is applicable to the process of forming anoxynitride film by performing nitriding as well as oxidation and to theprocess of forming a nitride film by performing only nitriding.

Although the present embodiment has described only the case where thethickness of a film is 2 nm or less, the present invention is notlimited thereto. It will be appreciated that the same effect as achievedin the present embodiment can also be achieved provided that therelationship between bedding strength and a film thickness has beenpredetermined even if the thickness of a film is 2 nm or more.

In principle, it is possible to use ellipsometry that has been usedconventionally instead of optical modulation reflectance spectroscopydescribed in the present embodiment in measuring a film thickness in theclustered manufacturing device. In contrast to ellipsometry whichrequires the provision of the polarizer and analyzer in the monitoringunit to measure a film thickness, as described above, optical modulationreflectance spectroscopy according to the present invention does notrequire the provision of the polarizer and analyzer. Hence, the use ofoptical modulation reflectance spectroscopy is not only advantageousover the use of ellipsometry in that the thickness of a thin film with athickness of 1.5 nm or less can be measured with high accuracy but alsoin terms of saving space, since the clustered manufacturing device hasonly a limited space.

EMBODIMENT 2

Next, a description will be given to a second embodiment related to thecontrol of the thickness of an oxide film during the formation of theoxide film. The present embodiment also assumes the use of the clusteredmanufacturing device according to the first embodiment, which is shownin FIGS. 1 and 2.

First, wafers to be processed including an advanced wafer (monitorwafer) are transferred from the load/unload port 6 into the load-lockroom 3 and cleaned in the cleaning chamber 1 under such conditions as toprovide “SPECTRUM FROM POST-CLEANING WAFER 1”. The wafers are then movedto the optical measurement chamber 5 in which measurement is performedby optical modulation reflectance spectroscopy.

After the natural oxide films are removed completely from the wafer, thewafers are subjected to oxidation which is performed by differentmethods for different times. Measurement by optical modulationreflectance spectroscopy is performed for each of the oxidationprocesses.

FIG. 5 is a spectral diagram showing the result of measurement performedby optical modulation reflectance spectroscopy in the presentembodiment. The film thicknesses shown in the drawing were determined byTEM observation. However, since the peak values in the drawing vary withthe SN ratio of the measurement system, as described above, theyindicate only relative values with respect to the film thicknesses. Asshown in the drawing, peaks were hardly observable in the spectraobtained from the wafers immediately after cleaning and the thicknessesof the oxide films were measured to be approximately 0 nm by TMEobservation.

FIG. 6 shows data indicative of the relationship between a filmthickness determined by TEM observation and a peak value of a spectrumobtained by optical modulation reflectance spectroscopy. As shown in thedrawing, the peak value of the spectrum increases as the film thicknessincreases till the thickness of the oxide film reaches a value close to2.0 nm. However, the peak value of the spectrum decreases after thethickness of the oxide film exceeds 2.0 nm, as shown in the drawing.

FIG. 7 is a TEM micrograph of a cross-sectional structure in which anoxide film with a thickness of 2.4 nm and a polysilicon film aredeposited on a silicon substrate. As shown in the drawing, the presentapplication has determined the thickness of the oxide film based on theresult of TEM observation performed with such a resolution with whichthe network structure of a silicon oxide film can be observed.

Next, a description will be given to the process of forming an oxidefilm with a thickness of 1.5 nm with reference to the data. First, awafer is introduced into a rapid thermal processing furnace 2 into whichO₂ gas is introduced at a flow rate of 500 sccm and heated to 1000° C.for about 1 minute. By properly adjusting the subsequent retention time,an oxide film with a desired thickness can be formed. In the experimentconducted in the present embodiment, an oxide film with a thickness ofabout 1.5 nm was obtained after the retention time of about 10 sec. Whenthe optical measurement system was used in the present embodiment, themanufacturing process was controlled by adjusting the peak value of thespectrum obtained by optical modulation reflectance spectroscopy toapproximately 1.8 shown in FIG. 6. As a result, only oxide films withvarying thicknesses of 1.5 nm±0.2 nm were formed in accordance with theconventional method using a clustered manufacturing device but not usingoptical measurement for a control operation. By contrast, oxide filmswith varying thicknesses of 1.5 nm±0.1 nm were formed in the experimentconducted in the present embodiment so that variations in the thicknessof the oxide film are limited to the range of ±0.1 nm.

If the oxide film remaining on the wafer after cleaning was detected inthe optical measurement chamber 5, the wafer is placed again in thecleaning chamber 1 so that cleaning is performed appropriately for thetime required to remove the remaining oxide film. This saves the waferwhich might have failed if it had been processed in the subsequent stepand allows effective use of the wafer.

The pass/fail judgment of the oxide film described above allows properprocedures to be followed, such as “advance the wafer to the subsequentprocess,” “perform an additional oxidation process,” and “remove theoxide film and perform again the whole process from the initialoxidation”.

As standard values for controlling the manufacturing process, valuesappropriate for the circumstances of the process and measurement systemare preferably used since whether the standard values are proper or notis determined by various factors.

The measurement method used in the present embodiment is not onlyapplicable to the clustered manufacturing device and method but also tothe conventional film thickness control after the oxidation process. Bythus incorporating the optical measurement method into the process offorming the insulating film, the film thickness can be determinedprecisely during the manufacturing process, so that the process ofmanufacturing an insulating film such as a gate insulating film iscontrolled more appropriately.

If the clustered manufacturing device is used, in particular, there canbe achieved the remarkable effect of judging whether each of the processsteps currently performed is proper or not by performing opticalevaluation in the clustered manufacturing device as in the presentembodiment, since the wafer cannot be retrieved from the clustereddevice till sequential process steps are completed. Since the surfacestate of the wafer is not affected by environmental conditions outsidethe device (the presence of oxygen, moisture, or the like), the presentinvention is advantageous in that it can determine the thickness of athin oxide film of 2 nm or less, while removing the influence of anatural oxide film or the like, thereby achieving higher measurementaccuracy.

Although the present embodiment has described only the case where thethickness of a film is 2 nm or less, the present invention is notlimited thereto. It will be appreciated that the same effect as achievedin the present embodiment can be achieved provided that the relationshipbetween bedding strength and a film thickness has been predeterminedeven if the thickness of a film is 2 nm or more.

In principle, it is possible to use ellipsometry that has been usedconventionally instead of optical modulation reflectance spectroscopydescribed in the present embodiment in measuring the film thickness inthe clustered manufacturing device. However, optical modulationreflectance spectroscopy is advantageous over ellipsometry for thereasons described above in the first embodiment.

Although the present embodiment has provided the rapid thermalprocessing chamber 2 to perform an oxidation process with respect to thewafer, if the relationship between a film thickness and a peak value ofa spectrum obtained by optical modulation reflectance spectroscopy ispredetermined, the present invention is also applicable to the processof forming an oxynitride film by performing nitriding as well asoxidation and to the process of forming a nitride film by performingonly nitriding.

EMBODIMENT 3

Although the optical measurement system for performing measurement byoptical modulation reflectance spectroscopy has been mounted on theoptical measurement chamber 5 in the clustered manufacturing device ineach of the first and second embodiments, the present invention is notlimited thereto. For example, the present invention is also applicableto the following manufacturing device which has not been clustered.

FIG. 9 is a cross-sectional view schematically showing a structure usedwhen optical measurement is performed in a single isolated chamber as anunclustered manufacturing device according to a third embodiment, e.g.,a reaction chamber 50 in which plasma CVD is performed. As shown in thedrawing, a cathode electrode 53 as a lower electrode and an anodeelectrode 54 as an upper electrode are disposed in the reaction chamber50. A wafer 22 made of p-type silicon is placed on the cathode electrode53. A silicon oxide film (not shown) is formed by CVD on a semiconductorregion 24 of the wafer 22. A plasma 55 is generated in the reactionchamber 50 by applying RF power from an RF power source 51 between theelectrodes 53 and 54 via a coupling capacitor 52. A wall surface of thereaction chamber 50 is provided with an endpoint detection window 57, aprobe light incident window 58, and a reflected light monitor window 59.

On the other hand, an endpoint detection system 59 and members formeasuring reflection intensity R are provided externally of the reactionchamber 50. As one of the members, there is provided a Xe lamp 61 forgenerating probe light with which the semiconductor region 24 isirradiated. Probe light 71 generated from the Xe lamp 61 is reflected bya mirror 61 to pass through the silicon oxide film on the wafer 22placed in the reaction chamber 50 via the probe light incident window 58and reach the semiconductor region 24. Reflected probe light 72 from thesemiconductor region 24 is extracted to the outside of the reactionchamber 50 from the reflected light monitor window 59 so that theintensity thereof is measured by a reflection intensity measurementsystem 66 (in particular, the region at a wavelength of about 376 nm andwith energy of about 3.3 eV). Data on the reflection intensity measuredby the reflection intensity measurement system 66 is transmitted to anetching control system 68 via a signal path 67. There is also providedan Ar ion laser 63 for generating exciting light with which thesemiconductor region 24 is irradiated. Exciting light 73 generated fromthe Ar ion laser 63 is chopped by a chopper 64 at a frequency of 200 Hzand transmitted intermittently. The exciting light 73 is supplied intothe reaction chamber 50 via the endpoint detection window 57 and usedfor intermittent irradiation of the semiconductor region 24. The value(ΔR/R) obtained by dividing, by the reflection intensity R in theabsence of the radiation of exciting light 73, the difference ΔR betweenthe reflection intensities of the reflected probe light 72 in thepresence and absence of the radiation of exciting light 73 is detectedas the change rate of reflectance by the reflection intensitymeasurement system 66. Optionally, a polarizer and an analyzer may alsobe disposed at the probe light incident side and at the probe lightreflecting side, respectively.

In the arrangement, a variation in the change rate of reflectionintensity is monitored in the reaction chamber in which an insulatingfilm is formed actually by CVD. Even in an unclustered manufacturingdevice which is a single isolated device for forming a film by CVD,sputtering, or thermal oxidation, therefore, the thickness of the formedfilm can be measured by using spectra obtained by optical modulationreflectance spectroscopy. In particular, measurement by opticalmodulation reflectance spectroscopy has the advantage of allowingmeasurement of large thicknesses which can be measured by currentlyprevalent ellipsometry only with a large measurement error or smallthicknesses which are so difficult to measure by ellipsometry that asufficient measurement sensitivity is unobtainable.

EMBODIMENT 4

Next, a description will be given to a fourth embodiment related tomeasurement by optical modulation reflectance spectroscopy performed inn-type and p-type semiconductor regions. As a manufacturing device andan optical measurement system to be used in the present embodiment,those used in the first or third embodiment may be used, though they arenot shown in the drawing. For convenience, the following descriptionwill be made of a measurement procedure to be followed when a clusteredmanufacturing device and an optical measurement system shown in FIGS. 1and 2 are used. However, the unclustered CVD device and opticalmeasurement system shown in FIG. 9 may also be used instead.

Relationship between Thickness of Oxide Film and Measurement DataObtained by Optical Modulation Reflectance Spectroscopy

First, wafers to be processed including an advanced wafer, each havingn-type and p-type semiconductor regions, were introduced from a loadroom 6 and cleaned by the method described above in the secondembodiment.

Next, respective surfaces of the wafers were oxidized such that oxidefilms were formed on the n-type and p-type semiconductor regions. Byvarying the oxidation time, measurement samples having differentthicknesses were formed and the thicknesses of the individual sampleswere measured by optical modulation reflectance spectroscopy.

FIG. 10 shows data indicative of the relationship between filmthicknesses determined by TEM observation and “peak-to-peak values” ofspectra obtained by optical modulation reflectance spectroscopy. In thedrawing, ▪ indicates measurement data on the oxide film on the p-typesemiconductor region and ▾ indicates measurement data on the oxide filmon the n-type semiconductor region. The “peak-to-peaks” value in FIG. 10shows the difference between the maximum value of a spectrum (positivepeak value) and the minimum value thereof (negative peak value).

FIG. 11 shows spectra before a noise removing process is performed withrespect thereto, which were obtained from actual measurement by opticalmodulation reflectance spectroscopy performed in the n-typesemiconductor region.

As shown in FIG. 10, the “peak-to-peak value” of the change rate ofreflectance (ΔR/R) is higher, i.e., measurement sensitivity is higher inthe p-type semiconductor region than in the n-type semiconductor regionwhen the thickness of the oxide film is about 1.0 nm or less. If thethickness of the oxide film is larger than about 1.0 nm, on the otherhand, the “peak-to-peak value” is higher in the n-type semiconductorregion. If the thickness of the oxide film is over 1.0 nm, thepeak-to-peak value tends to decrease in the p-type region.

If the thickness of the oxide film is close to 0.2 nm, a peak portioncan be found only with difficulty in the spectra in the n-typesemiconductor region due to indentations resulting from noise, as shownin FIG. 11.

The following is a summary of the foregoing data. As the thickness of agate insulating film increases, the number of electrons captured therebyincreases. The phenomenon occurs when the film thickness is in the rangeof 0 to 2 nm. As shown in FIG. 10, the increase in the change rate ofreflectance due to the increased number of captured electrons isparticularly remarkable when the thickness is 1 nm or more at thesurface of the n-type semiconductor region. On the other hand, thevariation in the change rate of reflectance due to the increased numberof captured electrons is remarkable when the thickness is in the rangeof 0.5 to 1.5 nm at the surface of the p-type semiconductor region.Although the varying property of signal intensity is dependent onconditions for the process of forming the film, data on the thickness ofthe film can be obtained from the varying property of signal intensity.

By using the measurement data in the p-type semiconductor region whenthe thickness of the oxide film is 1.0 nm or less, while using themeasurement data in the n-type semiconductor region when the thicknessof the oxide film is over 1.0 nm, in particular, precise measurementscan be made on almost all oxide films having thicknesses of 1.5 nm orless, which have been difficult conventionally to measure withprecision. The effect is achievable regardless of whether a clusteredmanufacturing device is used or not.

Control of Thickness of Oxide Film

Next, the result of effecting control of the thickness of an oxide filmwill be described with reference to data shown in FIG. 10.

Measurement by optical modulation reflectance spectroscopy was made on agate oxide film on each wafer and the manufacturing process wascontrolled such that the peak-to-peak value of the spectrum from eachwafer becomes a value corresponding to a thickness of 1.5 nm shown inFIG. 10.

FIG. 12 shows data indicative of variations in leakage current in a gateoxide film controlled by a method of controlling the thickness of a gateoxide film in the present embodiment. In the drawing, the horizontalaxis represents a wafer number and the vertical axis represents avariation (%) expressed as the ratio of an actually measured value tothe standard value of a gate leakage current. ◯ indicates measurementdata on a gate leakage current in a device formed by a manufacturingprocess in which the control method according to the present embodimenthas been incorporated and  indicates a gate leakage current in a deviceformed by a conventional manufacturing process in which the controlmethod according to the present embodiment has not been incorporated. Asshown in the drawing, variations in the thicknesses of the gate oxidefilms formed by using the control method of the present embodiment aresmall, so that variations in gate leakage current are also suppressed.

In the empirical conventional method, variations in the thicknesses ofgate oxide films increase as the operational time of the manufacturingdevice increases in the process of forming the gate oxide films eachhaving a thickness on the order of 1.5 nm, so that defects frequentlyoccur in the gate oxide films. In accordance with the method ofcontrolling the thicknesses of gate oxide films of the presentembodiment, however, variations in gate leakage current can be reducedso that the occurrence of defects in the gate oxide films is alsosuppressed. Thus, the method of determining a film thickness and themethod of manufacturing a semiconductor device implement ahigh-performance device having a gate insulating film with a thicknesson the order of 1.5 nm.

Control of Cleaning Process

Next, a description will be given to the result of measuring thethickness of an oxide film by using optical measurement in each ofp-type and n-type semiconductor regions in a cleaning process (involvingthe action of removing an oxide film) corresponding to the firstembodiment.

In that case, wafers to be processed including an advanced wafer(monitor wafer) are transferred from the load/unload port 6 to theload-lock room 3, similarly toe the cleaning process in the firstembodiment, and then cleaned in the cleaning chamber 1 for differenttimes. At this time, the surfaces of the wafers are etched with radicalsproduced by dissociating Cl₂ gas under the radiation of light to form aflat interface. For this purpose, anticorrosive treatment or the likehas been performed with respect to the surface of the cleaning chamber1.

Next, the cleaned wafers are transferred to the optical measurementchamber 5 and subjected to optical measurement by optical modulationreflectance spectroscopy using the optical measurement system shown inFIG. 2.

FIG. 13 shows data representing variations in the “peak-to-peak value”of the spectra obtained by optical modulation reflectance spectroscopyplotted against a cleaning time when the wafers are cleaned by using theclustered device shown in FIGS. 1 and 2. In the drawing, ▪ indicates avalue measured in the p-type semiconductor region and  indicates avalue measured in the n-type semiconductor region. Although dataobtained from the n-type semiconductor region is seemingly differentfrom the data shown in FIG. 4, this is because different methods ofprocessing data are used in FIGS. 4 and 13. Basically, the two sets ofdata show the same tendency. It will be understood that, in each of theregions, the film thickness is large when the cleaning time isinsufficient and the oxide film has not been removed sufficiently andthe film thickness is reduced when sufficient cleaning has beenperformed.

If the two sets of data obtained from the n-type and p-typesemiconductor regions are compared with each other, the peak-to-peakvalue is higher in the n-type semiconductor region till the cleaningtime reaches 3.0-4.0×10² sec. If the cleaning time exceeds 3.0-4.0×10²sec, however, the peak-to-peak value is higher in the p-typesemiconductor region. This indicates that the use of data obtained fromthe n-type semiconductor region achieves higher measurement sensitivityand higher measurement accuracy if the cleaning time is insufficient andthe oxide film is not so thin but the use of data obtained from thep-type semiconductor region achieves higher measurement sensitivity andhigher measurement accuracy if the cleaning time becomes longer and theremoval of the oxide film proceeds. The tendency coincides with thetendency shown in the data of FIG. 10.

In the cleaning process, therefore, cleaning involving the removal ofthe oxide film can be performed as necessary and sufficiently bycontrolling cleaning conditions and cleaning time, while makingmeasurement by optical modulation reflectance spectroscopy on the n-typeand p-type semiconductor regions and monitoring the thickness of oxidefilm based on data (ΔR/R) representing a higher sensitivity.

If variations in values measured during the formation of the oxide filmby thermal oxidation or CVD are estimated from the data shown in FIG.13, it will be understood that the measured values form a characteristiccurve with an inclination opposite to that of the characteristic curveshown in FIG. 13 when plotted against the lapse of processing time. Bythus using the data shown in FIG. 13, the thicknesses of a thermal oxidefilm and a CVD oxide film formed on the p-type and n-type semiconductorregions can also be controlled during the film formation process.

OTHER EMBODIMENTS

Although the first and second embodiments have arranged the cleaningchamber 1, the rapid thermal processing chamber 2 for forming the oxidefilm, the cooling chamber 4, and the optical measurement chamber 5around the load-lock room 3 in the clustered manufacturing device suchthat wafers are transferred under reduced pressure without being exposedto an external space between the individual chambers, as shown in FIG.1, the present invention is not limited thereto. By way of example,clustered manufacturing devices with the following structures can beused instead of the device shown in FIG. 1.

First, instead of separately providing the optical measurement chamber5, an optical measurement system may also be provided in the wafercooling chamber 4.

Second, instead of providing the rapid thermal processing chamber 2, achamber for forming an oxide film, a nitride film, and a polysiliconfilm by sputtering or CVD may also be provided.

Third, in addition to the rapid thermal processing chamber 2, a chamberfor forming an oxide film, a nitride film, and a polysilicon film bysputtering or CVD may also be provided. In particular, if a polysiliconfilm can be formed within the manufacturing device after the formationof the gate oxide film, a polysilicon film composing a gate electrodecan be formed advantageously before a natural oxide film is formed onthe wafer formed with a gate oxide film.

It is also possible to provide a part of a wafer with a monitor regionin which a semiconductor device as a product is not formed so that theforegoing optical measurement is performed with respect to thesemiconductor region within the monitor region. In that case,measurement sensitivity can be increased by achieving a higher impurityconcentration in the semiconductor region within the monitor region thanin the semiconductor region within the product semiconductor device.Since the monitor region with a large area can be provided, it has theadvantage of allowing easy optical measurement.

As a film having a thickness that can be measured by optical modulationreflectance spectroscopy according to the present invention, a filmcomposed of a material having the property of transmitting light(including UV light) may be used appropriately. Accordingly, the filmused in the present invention is not limited to an insulating film suchas an oxide film. Instead, a film composed of a transparent conductivematerial or a light-transmitting metal film may also be used. Since athinner film is more likely to transmit light even though it is made ofthe same material, restrictions on-materials to which the presentinvention is applicable are reduced.

As a structure of the optical measurement system suitable for use in aclustered manufacturing device, the following embodiment may also beused.

FIG. 14 is a cross-sectional view showing an exemplary structure inwhich the optical measurement system is disposed collectively on theceiling side of the chamber. As shown in the drawing, the entire opticalsystem is disposed on the ceiling side of the optical chamber 5connecting to the load-lock room 3 in the clustered manufacturingdevice. Specifically, a quartz window 23 for transmitting measuringlight and exciting light is mounted on the ceiling side of the opticalmeasurement chamber 5. On the quartz window 23, an incident measuringlight inlet 24 and a reflected measuring light outlet 25 are mounted.There are also provided: an exciting light source 7 (Ar ion laser); ameasuring light source 8 (150 W Xe lamp); an optical detector 9 formeasuring the intensity of reflected measuring light; an optical fiber11 for guiding the measuring light from the measuring light source 8 tothe measuring light inlet 24; an optical fiber 12 for guiding light fromthe measuring light outlet 25 to the optical detector 9; a chopper 28for intermittently irradiating an object under measurement with theexciting light at a frequency of 500 Hz generated from the excitinglight source 7 (modulation); a control/analyze system 13 having amonitor, a PC, or the like for controlling equipment andcalculating/analyzing data during measurement by optical modulationreflectance spectroscopy; and a signal line 30 for providing aconnection between the chopper 28 and the PC of the control/analyzesystem 13. Each of the incident measuring light inlet 24 and thereflected measuring light outlet 25 has the function as an optical fibersupporter. A wafer 22 is placed on a wafer stage 21 disposed in theoptical measurement chamber 5 such that measurement by opticalmodulation reflectance spectroscopy as described above is performed.

FIG. 15 is a cross-sectional view showing an exemplary structure inwhich measuring light is incident at a large angle on a sample undermeasurement. As shown in the drawing, a quartz window 23 fortransmitting measuring light and exciting light is mounted on theceiling side of an optical measurement chamber 5. On the quartz window23, an optical fiber supporter 44 for introducing exciting light ismounted. On the lateral sides of the optical measurement chamber 5,there are disposed an optical fiber supporter 40 for introducingmeasuring light, a measuring light inlet 41, a measuring light outlet42, and an optical fiber supporter 43 for releasing measuring light.Externally of the clustered manufacturing device, there are provided anexciting light source (Ar ion laser), a measuring light source (150 W Xelamp), and an optical detector for measuring the intensity of reflectedmeasuring light, though they are not shown in the drawing. There arealso provided: an optical fiber 10 for guiding light from the excitinglight source to the optical fiber supporter 44 for introducing excitinglight; an optical fiber 11 for guiding light from the measuring lightsource to the optical fiber supporter 40 for introducing measuringlight; and an optical fiber 12 for guiding light from the optical fibersupporter 25 for releasing measuring light to the optical detector. Theexciting light is used for intermittent irradiation of the sample undermeasurement at a frequency of 500 Hz by a chopper placed at a positionnot shown. There is also disposed a control/analyze system having amonitor, a PC, and the like for controlling equipment andcalculating/analyzing data during measurement by optical modulationreflectance spectroscopy.

FIG. 16 is a cross-sectional view showing an exemplary structure inwhich an optical measurement system is mounted more collectively on theceiling side of an optical measurement chamber 5. A quartz window 23 ismounted on the ceiling side of the optical measurement chamber 5. Aspherical member 45 is mounted on the quartz window 23. The surfaceconfiguration of the spherical member 45 is generally coincident with aspherical surface centering around the portion of the wafer 22 undermeasurement. On the spherical member 45, there are mounted: an opticalfiber supporter 40 for introducing measuring light which supports anoptical fiber; an optical fiber supporter 41 for releasing measuringlight which supports an optical fiber 12; and an optical fiber supporter44 for introducing exciting light which supports an optical fiber 10.The optical fiber supporter 40 for introducing measuring light and theoptical fiber supporter 41 for releasing measuring light are movablealong the slope of the spherical member 45, while constantly maintainingthe respective tilt angles from the perpendicular at the same value bymeans of a rack and pinion mechanism or the like. The optical fibersupporter 40 for introducing measuring light and the optical fibersupporter 41 for releasing measuring light are structured such that therespective tilt angles from the perpendicular are adjustable byactivating the rack and pinion mechanism under remote control from theoutside of the clustered manufacturing device. In other words, theoptical fiber supporter 40 for introducing measuring light and theoptical fiber supporter 41 for releasing measuring light are structuredsuch that the angle of incidence of the measuring light on the wafer 22on the wafer stage disposed in the optical measurement chamber 5 isadjustable. In such a structure, the light inlet/outlet portions of theoptical measurement system can be disposed collectively in an extremelylimited space so that the structure is mounted particularly suitably ona clustered manufacturing device.

What is claimed is:
 1. A method of manufacturing a semiconductor device,including formation of a film on a semiconductor region of a wafer orremoval of a film from a surface of the semiconductor region of thewafer, the method comprising the steps of: (a) irradiating thesemiconductor region of the wafer with measuring light; (b)intermittently irradiating the semiconductor region of the wafer withexciting light; and (c) calculating a change rate of reflectance bydividing the difference between the reflectances of the measuring lightwhen the semiconductor region of the wafer is irradiated and notirradiated with the exciting light by the reflectance of the measuringlight when the semiconductor region is not irradiated with the excitinglight, wherein the thickness of the film is determined based on thechange rate of reflectance.
 2. The method of manufacturing asemiconductor device according to claim 1, wherein the step (c) includesproducing a spectrum indicative of the change rate of reflectance whenthe wavelength of the measuring light is varied and determining thethickness of the film based on a peak value which is a maximum absolutevalue of the change rate of reflectance.
 3. The method of manufacturinga semiconductor device according to claim 1, wherein the step (c)includes producing a spectrum indicative of the change rate ofreflectance when the wavelength of the measuring light is varied anddetermining the thickness of the film based on a peak-to-peak valuewhich is the difference between a positive maximum value of the changerate of reflectance and a negative maximum value thereof.
 4. The methodof manufacturing a semiconductor device according to claim 1, whereinthe step (c) includes determining the thickness of the film based on thechange rate of reflectance at a constant wavelength close to thewavelength of the measuring light indicative of a peak value which is amaximum absolute value of the change rate of reflectance.
 5. The methodof manufacturing a semiconductor device according to claim 1, whereinthe thickness of the film is 2 nm or less.
 6. The method ofmanufacturing a semiconductor device according to claim 5, wherein theoptical evaluation is performed with respect to a p-type semiconductorregion as the semiconductor region when the thickness of the film is 1nm or less.
 7. The method of manufacturing a semiconductor deviceaccording to claim 1, wherein the thickness of the film is measured ineach of a p-type semiconductor region and an n-type semiconductor regionas the semiconductor region and the value measured based on the higherchange rate of reflectance in the p-type semiconductor region or in then-type semiconductor region is used as the thickness of the film.
 8. Themethod of manufacturing a semiconductor device according to claim 7,wherein the semiconductor region has a resistivity of 0.1 Ωcm⁻¹ or less.